Rock Cycle

The Rock Cycle

The Earth's outer solid layer, the lithosphere, is made of rock.

The rocks you see around you - the mountains, the valleys, the sea shore and the riverbeds are all made of minerals.

A rock is made up of two or more minerals. You need minerals to make rocks, but you don't need rocks to make minerals. All rocks are made of minerals.

What is a mineral?

Minerals are solids and inorganic. They occur naturally and have a definite chemical formula. They all have their own general structure. Almost all chemical elements in the Earth's crust are associated with at least one mineral.

Minerals vary in colour, hardness, density, crystal form, crystal size, transparency, composition, location, and abundance. Some minerals are radioactive (uranophane), while others are magnetic (magnetite). Some minerals are pure – we call them elements. Examples such as gold, silver, sulphur, lead, tin, iron, bismuth, copper and platinum fall into this category.

The concept of the rock cycle is attributed to James Hutton (1726—1797), the 18th-century founder of modern geology. The main idea is that rocks are continually changing from one type to another and back again, as forces inside the earth bring them closer to the surface (where they are weathered, eroded, and compacted) and forces on the earth sink them back down (where they are heated, pressed, and melted). So the elements that make up rocks are never created or destroyed — instead, they are constantly being recycled. The rock cycle helps us to see that the earth is like a giant rock recycling machine!

What Rocks?

There are three main types of rock; igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, and petrology is an essential component of geology.

Igneous Rock

Igneous rocks are called fire rocks and are formed either underground or above ground. Underground, they are formed when the melted rock, called magma, deep within the earth becomes trapped in small pockets. As these pockets of magma cool slowly underground, the magma becomes igneous rocks.

Igneous rocks are also formed when volcanoes erupt, causing the magma to rise above the earth's surface. When magma appears above the earth, it is called lava. Igneous rocks are formed as the lava cools above ground.

Sedimentary Rocks

For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn away by wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.

Metamorphic Rocks

Metamorphic rocks are rocks that have "morphed" or changed into another kind of rock. These rocks were once igneous or sedimentary rocks. How do sedimentary and igneous rocks change? The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change. If you exam metamorphic rock samples closely, you'll discover how flattened some of the grains in the rock are.

Rock and Mineral examples

Serpentine is a major rock forming mineral and is found as a constituent in many metamorphic and weather igneous rocks. It often colours many of these rocks to a green colour and most rocks that have a green colour probably have serpentine in some amount.

Cinnabar is a colorful mineral that adds a unique color to the mineral color palette. Its cinnamon to scarlet red color can be very attractive. Well shaped crystals are uncommon and the twinned crystals are considered classics among collectors. The twinning in cinnabar is distinctive and forms a penetration twin that is ridged with six ridges surrounding the point of a pryamid. It could be thought of as two scalahedral crystals grown together with one crystal going the opposite way of the other crystal. Cinnabar was mined by the Roman Empire for its mercury content and it has been the main ore of mercury throughout the centuries. Some mines used by the Romans are still being mined today. Cinnabar shares the same symmetry class with quartz but the two form different crystal habits

Schist is a medium grade metamorphic rock, formed by the metamorphosis of mudstone / shale, or some types of igneous rock, to a higher degree than slate, i.e. it has been subjected to higher temperatures and pressures. The resulting foliation is coarser and more distinct than that of slate due to the higher degree of crystallisation of mica minerals (biotite, chlorite, muscovite) forming larger crystals, and is often referred to as schistosity.

Marble is a metamorphic rock form composed of coarse crystals from parent limestone or dolostone rocks. Pure marble is white and composed of the mineral calcite. It has been very popular for sculpture and building construction because of its beauty and relative softness. It is vulnerable to weathering since its calcium carbonate content is readily attacked by acid rain

Diorite is a coarse-grained, intrusive igneous rock that contains a mixture of feldspar, pyroxene, hornblende and sometimes quartz.

Quartz is the most common mineral found on the surface of the Earth. A significant component of many igneous, metamorphic and sedimentary rocks, this natural form of silicon dioxide is found in an impressive range of varieties and colours. There are many names for different varieties: Cryptocrystalline varieties of quartz are listed separately under chalcedony, and include agate.

Granite rocks are igneous rocks which were formed by slowly cooling pockets of magma that were trapped beneath the earth's surface. Granite is used for long lasting monuments and for trim and decoration on buildings.

Jasper is an opaque and fine-grained quartz. Colored red, yellow, brown, or off-white to gray by impurities, jasper has long been used as an ornamental stone because it takes a fine polish. The color of a streak made on a black jasper touchstone can determine with good accuracy the gold content of gold ores

Feldspar is by far the most abundant group of minerals in the earth's crust, forming about 60% of terrestrial rocks. Most deposits offer sodium feldspar as well as potassium feldspar and mixed feldspars. Feldspars are primarily used in industrial applications for their alumina and alkali content. The term feldspar encompasses a whole range of materials. Most of the products we use on a daily basis are made with feldspar: glass for drinking, glass for protection, fiberglass for insulation, the floor tiles and shower basins in our bathrooms, and the tableware from which we eat. Feldspar is part of our daily life.

Pyrite crystal usually forms as a cube with fine ridges (striations) on the crystal's faces. Less commonly, it forms as octahedrons (eight-sided shapes), nodules, or massive forms. It can also occur as coarse granules.

Pyrite is called fool's gold because its brassy yellow color is very similar to gold. Although it looks like gold, its other physical properties are very different. Pyrite is harder, less dense, and more brittle. It leaves a greenish-black streak while gold leaves a golden-yellow one. However, pyrite is often associated with the presence of gold and copper, and locating fool's gold may mean the real thing isn't far off.

Interactive

Reading and Worksheets

Activities

Readings

Videos

Rock Cycle Song

(Sing to the tune of "Row, Row, Row Your Boat")

SEDIMENTARY rock

Has been formed in layers

Often found near water sources

With fossils from decayers

Then there's IGNEOUS rock

Here since Earth was born

Molten Lava, cooled and hardened

That's how it is formed

These two types of rocks

Can also be transformed

With pressure, heat and chemicals

METAMORPHIC they'll become.

( Don't forget to sing this as a "Round"; after all, it is the Rock "Cycle"! )

Soil

Soils are complex mixtures of minerals, water, air, organic matter, and countless organisms that are the decaying remains of once-living things. ... The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.